I followed all the steps listed. But, when I tried to "add" CS5 to the nVidia Control Panel, I browsed to the PremPro exe and hit "open", but it didn't add it to the list. All the CS4 programs are there, but no CS5.

Bear in mind that the GTX 295 is a dual-GPU card. But Premiere Pro CS5.x currently supports only one GPU - and future Premiere Pro CS releases will continue to support only single GPUs for the foreseeable future. As a result, your GTX 295 gets half-unused every time you run CS5 in GPU-accelerated mode, which ends up with that GTX 295 being as slow as a GTX 260 or GTX 275.